J heads

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Further, let me add that small block heads interchange, with just a few small details including early 273 heads having different intake bolt hole angles, 2.02 heads on a stock 273 is a "oh oh" (bore size), and of course magnum heads will go on the older LA also but some mods will need to be done
In short, 318, 340 & 360 LA heads are all interchangeable as far as bolt on.
 
Shamrock--WV2NC said:
I'm going to look at a couple engine blocks this weekend. One is a 340. Do j heads fit on a 340? Or are j heads for 360? Thanks
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What direction are you going here? There are a few different combinations that you don't want to mix. A engine wit a 8.5/1 compression ratio and a closed chamber head will loose compression by installing a open chambered head. You need the correct combination for it to work.
 
I went to buy a 360 from a Dude and it wouldn't spin. I tried using a breaker bar but it would not move. So I found this 340 block close to me and wanted to check it out. The guy also has a 360 block and a set of j heads. I'm gonna try to get a deal on the 340 and heads. That's my plan at the moment.
 
Shamrock--WV2NC said:
I went to buy a 360 from a Dude and it wouldn't spin. I tried using a breaker bar but it would not move. So I found this 340 block close to me and wanted to check it out. The guy also has a 360 block and a set of j heads. I'm gonna try to get a deal on the 340 and heads. That's my plan at the moment.
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Don't worry about closed chambers.
Aside from that, they're blocks...right?
Put whatever piston you want in it.
 
If you're going to rebuild it you will (should) put what ever pistons needed for the heads you will use. Talk to your machine shop or do some homework here to see what works.
 
I have 360 J heads on my 318. Did domed pistons and ended up with them being .08 below deck.. still can run 92 pump gas and they work awesome.. there are a couple different chamber sizes.. mine are 72cc with 1.88 intake valves. Will they work?? Hell yeah...
 
In fact, if you take a J head and have 2.02 intake valves installed, you pretty much have early 340 X heads.
 
When you get towards the "all out effort" I have been told that x heads are good for about 10-12 cfm more than J's. The reason being the j's were originally designed for the smaller valve. So the water is closer and you have to be more conservative than with the x's. Again at the max effort level.
 
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